-2 geometric current density / A m

Thomas Maskow

Department Umweltmikrobiologie Thomas.maskow@ufz.de

Nachhaltige Energieerzeugung mittels Biotechnologie

Stand (15.12.2014)

State of the art in „white biotechnology“

?

Cells Substrate

CO₂ Products new cells

Y_S/X C_S1H_S2O_S3 + Y_N/X NH₄⁺+ Y_O/X O₂ Y_CO2/X CO₂ + C_X1H_X2O_X3N_X4 + Y_P/X C_P1H_P2O_P3N_P1

(CH_1.84O_0.53N_0.23)

Product P

Substrate S Biomass X

Why waste of energy?

O₂ + H⁺

4 e^- 2 H₂O

Cell

Microbial fuel cells (Electrons not to oxygen to electrode)

 General Principles

 History

 The energy metabolisms of microorganisms

 The most important bottleneck of MFC

 Factors limiting the electrical energy generation

 Microbial electrolyses cells (MEC)

 Other bulk chemicals using (MFC/BES) ?

 Pro and con of MFC, MEC or BES

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General principle of microbial fuel cell

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O

+ 4 H

+ 4 e

->

2 H

O

Brief history of microbial fuel cell

1911 M.C. Potter (University of Durham): Electricity from E. coli 1931 Barnet: MFC connected in series -> 35 volts but just 0.2 mA 1963 DelDuca et al.: used hydrogen (from fermentation of glucose

by Clostridium butyricum) as the reactant for a „normal fuel cell“; Problem: unreliable due to unstable H₂ production, indirect MFC

1976 Suzuki: Solved the problem with unstable H₂ production 1976 Suzuki et al.: Current design concept of an MFC

Seventies Suzuki et al.: Some basics of function of MFC revealed Seventies MJ Allen, H. Peter Bennetto (King‘s College London):

MFC -> generation of electricity for third world countries.

May 2007 University of Queensland, Australia; prototype MFC; The prototype (10 L) converts the brewery waste water into CO₂, clean water, and electricity. 660 gallon waste water -> 2 kilowatts; Negligible amount of power but clean

water

The energy metabolism of microorganims

   





F x n

G^'  ^'  ^'



1

' 2894.55 ^

 

G kJmol

Due to:

 Side reaction at the cathode (impurities in the electrolyte and at the electrode surface)

 Mixed potentials are formed

 ^V

mol s A x

G ^' 24 96485.3 ¹ 0.430.82

 ^{ }

1

' 2894.55 ^

  

G kJ mol

 ^V

mol s A x

G ^'  24 96485.3 ¹ 0.430.51

 ^{ }

1

' 2176.70 ^

 

G kJ mol

' . '

' .







   

 G

G

G

   





F n

G_total^'  ^' cos , ₂  ^' 1/2 ₂, ₂



   





F n

G_biol^'  ^' cos , ₂  ^'



   





F n

G_elec^' _.  ^'  _effective^' 1/2 ₂, ₂



 A part of the

energy is „wasted“

to biomass !!!

 E

(link) determines

the electrical energy

available!!!

The most important bottleneck of MFC ???

Transport of the electrons to the anode ?

A number of hypotheses have been proposed which explain how an efficient electron transfer from the microbial cells to the fuel cell anode can be achieved:

Direct electron transfer (DET): a, b

Mediated electron transfer (MET): c, d

Direct electron transfer (DET):

Physical contact between microorganism and anode material is necessary.

The link are cytochromes

Direct electron transfer (DET):

Physical contact between microorganism and anode material is necessary.

(a) Direct electron transfer via membrane bound cytochromes.

(b) Electron transfer via microbial nanowires:

 Most straightforward electron transfer mechanism (the whole bacterial cell is adherent to the anode)

 Ascribed to a number of microorganisms (e.g. Geobacter, Rhodoferax)

 Direct cell contact to the fuel cell anode confines the number of electro- chemically active cells to a

mono-layer

maximum current densities (to e.g., 3 µA cm

)

 Recently found (2005)

 Ascribed to the Geobacteraceae and species of the Shewanella family

 Electron transfer via a conductive “pili”; work over several microbial layers.

 Increase the

achievable current

one order of magnitude

1998 2000 2002 2004 2006 2008 2010 0

5 10 15 20 25 30

geometric current density / A m-2

year of publication (II) Electrode Development

(I)  Biocatalyst Development

(I)

(II) Recent progress of BES anode current densities …. 

Mono-layer

Transmission electrone microscopy analysis Wild type Geobacter sulfurreducens

Geobacter sulfurreducens ∆pilA

0.2 µm 0.2 µm

20 µm

Fe³⁺ + e^- -> Fe²⁺

Pili

 ^V

mol s A x

G_elec^'  24 96485.3 ¹ 0 0.51

 ^{ }

   





F x n

G_elec^'  ^'  ^' 0.5 ₂/ ₂



1

' 1181 ^

  

G_elec kJ mol

A maximum of 54 % of the energy can be got

Mediated electron transfer (MET):

Physical contact between microorganism and anode material is necessary.

(a) MET via exogenous (artificial) redox mediators

 current densities (3 – 30 µA cm^-2) (10 -100 µA cm^-2)

 regular addition of sometimes harmful substances

V E^' /

Redoxpotential in

Mediated electron transfer (MET):

Physical contact between microorganism and anode material is necessary.

(b) MET via secondary metabolites

V E^' /

Redoxpotential in

 current densities (10 -100 µA cm^-2)

 no addition of redox mediators required

 the efficiency of current generation higher due to higher redox potential in comparison to cytochromes

SEITE 18

 ^V

mol s A x

G_elec^' 24 96485.3 ¹ 0.110.51

 ^{ }

   





F x n

G_elec^'  ^'  ^' 0.5 ₂ / ₂



1

' 1447 ^

  

G_elec kJ mol

66 % energy efficiency possible

Weaknesses:

 potential loss of mediators ->

decreasing in n and thus coulombic and energetic efficiency

 Synthesis and replacement of this components energetically expensive

Mediated electron transfer (MET):

Physical contact between microorganism and anode material is necessary.

(c) MET via primary metabolites

 Any terminal electron acceptor applicable if:

+ redox potential sufficiently negative to that of oxygen, + water soluble in oxydized and reduzed form,

+ reversibly oxidizable

O H S

e H

SO

Anode Bacteria

2 2

2

4 8 8  4



 







 

 

 ^{  }



mV E ^'  220

 ^ G_elec^' _,n1  70.4kJ mol^1 G_elec^'  1690 kJ mol^1

Maxium energy efficiency = 77.6 %

via anaerobic respiration

via fermentation

2 2

3 2

6 12

6H O 2 H O 2CH COOH 2 CO 4H

C    

Maximum energy efficiency = 33 %

 Perfect negative potential

 But low because only 8 electrons (4H₂) are formed

 ^V

mol s A x

G_elec^' 8 96485.3 ¹ 0.42 0.51

 ^{ }

   





F x n

G_elec^'  ^'  ^' 0.5 ₂ / ₂



1

' 718 ^

 

G_elec kJ mol

What is the best electron transfer ?

DET:

MET:

 High coulombic efficiencies

 Low current and power densities

 Requires extremely large anodic surfaces

 The involved microorganisms (e.g. Geobacter) call for low molecular substances (i.e. acetate, butyrate etc.)

 low coulombic efficiency due to formation of electrochemically inactive side products

 High current and power densities

 High diversity of exploitable microorganisms

 Big variety of utilizable substances

Physical factors limiting the electrical energy generation

1. Electrical parameters

Voltage

Power (E x I) E

x I P  

RExt

x I E 





Ext  R

Open circuit voltage

 0 RExt

Short circuit conditions Optimum

External load matches internal resistance

A - Activitation loss

Cathodic (E^cathode) and anodic (E^anode) polarization curve. ∆E – cell voltage; 1.ΣR_Ω ohmic losses

B - Ohmic loss E = R x I

C - Mass transfer loss

Mass transfer loss:

 Substrate rate to the anodic biofilm limits the rate of current generation

 Oxygen rate to the cathode surface limits the rate of current generation

 Prevention of accumulation of waste products (e.g. oxidized intermediates or protons)

 Proton accumulation leads to

pH-gradient affecting the MFC

performance

Ohmic loss

 Resistance of the electrode material

 High conductivity of the material

 Conductivity, buffer capacity,

minimal distance between electrodes are of uttermost importance

 Short travel distances for the electrode

Activation loss

Energy barrier:

to start electron transfer to the anode or cathode

Low activation losses by:

 Bacteria can optimize their electron transferring strategies

 Increasing the operating temperature

 Establishment of an enriched biofilm on the electrode

 Increasing electrode surface

Electron quenching reactions and energy efficiency

 Loss of electrons due to alternative reactions

(e.g. Methanogenesis, respiration (if oxygen intrudes))

 Loss by formation of anodophilic biomass such losses measured as coulombic efficiency (CE)

Coulombic efficiency (CE):

Electrons recovered/ available electrons Potential efficiency (PE):

actual voltage (∆E)/OCV

Energy conversion efficiency (ECE):

CE x PE

Bruce Logan Hong

Liu

Other bulk chemicals using (MFC/BES) ?

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O₂ + 4 H⁺ + 4 e^- ->2 H₂O (1 157 mV)

Other bulk chemicals using (MFC/BES) ?

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O₂ + 4 H⁺ + 4 e^- ->2 H₂O (1 157 mV) O₂ + 2 H⁺ + 2 e^- ->H₂O₂ ( 623 mV)

Other bulk chemicals using (MFC/BES) ?

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O₂ + 4 H⁺ + 4 e^- ->2 H₂O (1 157 mV) O₂ + 2 H⁺ + 2 e^- ->H₂O₂ ( 623 mV) CO₂ + 8 H⁺ + 8 e^- ->2 H₂O + CH₄ ( 98 mV)

Other bulk chemicals using (MFC/BES) ?

Methan production unsing BES (bioelectrochemical systems)

Methane formation and loss of carbon dioxide at a set potential of -1.0 V (100 mM PBS saturated with CO₂).

Bruce E. Logan, Shaoan Cheng and Defeng Xing with a microbial cell that produces methane directly from electricity.

Methan production unsing BES (bioelectrochemical systems)

According to the expectations, the processes happens in

biofilms.

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O₂ + 4 H⁺ + 4 e^- ->2 H₂O (1 157 mV) O₂ + 2 H⁺ + 2 e^- ->H₂O₂ ( 623 mV) CO₂ + 8 H⁺ + 8 e^- ->2 H₂O + CH₄ ( 98 mV)

Other bulk chemicals using (M?C) ?

2 H⁺ + 2 e^- -> H ( - 76 mV)

C

H

O

+ 6 H

0 ->

6 CO

+ 24 H

+ 24 e

O₂ + 4 H⁺ + 4 e^- ->2 H₂O (1 157 mV) O₂ + 2 H⁺ + 2 e^- ->H₂O₂ ( 623 mV) CO₂ + 8 H⁺ + 8 e^- ->2 H₂O + CH₄ ( 98 mV)

Other bulk chemicals using (M?C) ?

2 H⁺ + 2 e^- -> H₂ ( - 76 mV)

Hydrogenproduction using

microbial catalysis

Basic Idea: CH₃C00^-

CH₄ + HCO₃^-

Conventional ∆G^o = -28.5 kJ mol^-1 -55,6 kJ g^-1

+ H₂0

i MFC

+ 0.14 V (theoretical) + 0.22 V (practical)

-890 kJ mol^-1

∆G^o = 104 kJ mol^-1

Thermodynamically impossible 4 H₂ + 2 HCO₃^-+ H⁺

-143 kJ g^-1

+ 4 H₂0 4 x -286 kJ mol^-1 = -1144 kJ mol^-1

 28 % more energy gained

 H₂ wears more energy

E F

n

G  



but

• Electrohydrogenesis or biocatalyzed electrolysis is the name given to a process for generating hydrogen gas from organic matter being decomposed by bacteria.

• This process uses a modified fuell cell, 0.2 - 0.8 V of electricity is used,

• Energy efficiency of 288%

Inverse MFC (i-MFC), Electrohydrogenesis, Biocatalysed Electrolysis, Microbial

Electrolysis Cell (MEC)

2004

Biocatalysed electrolysis: <1.0 kWh/Nm³ H₂; Water electrolysis: >4.5 kWh/Nm³ H₂

Realistic target: > 10 Nm³ H₂/m³ of reactor volume/day ∆E = 0.3 - 0.4 Volt.

Hydrogen production efficiencies: >90%

Summary

Other sources of biohydrogen

 Why is hydrogen important?

 Fermentative hydrogen production

 Hydrogen from sunlight

Why is hydrogen important and environmentally friendly?

 Hydrogen can be produced domestically, cleanly and cost-effectively from a variety of resources (

sunlight, biomass and water

 Hydrogen (other as bioethanol or methane) combusted simply to water;

No green house effect

 Hydrogen can be efficiently converted into electricity using fuel cells (efficiency approx.

50 %;

20%

 Energy density (J/g)

>

 But energy density (J/m³)

<



No NOx emission

Fermentative hydrogen production?

H₂

Butyrate Acetate

Succinic acid

Fermentative hydrogen production?

4 mol H2 per mol Glucose too low to be economically viable !!!

Real yields between:

0.52 (1998) from molasses using Enterobacter aerogens 3.8 (2001) from glucose using Enterobacter cloacae DM11

Hydrogen from sunlight?

1939 - German researcher (Hans Gaffron, University of Chicago), that algae can switch between producing oxygen and hydrogen.

1997 - Anastasios Melis - deprivation of sulfur will cause the switch; the enzyme, hydrogenase, responsible for the reaction.

2006 - Researchers from the University of Bielefeld + University of Quensland have genetically qualified the green alga Chlamydomas reinhardtii to produce large amounts of hydrogen. 5 x more as the wild type; energy efficiency: 1.6 - 2.0 % 2007 - Discovered: if copper is added to block oxygen generation -> algae will switch

to the production of hydrogen

2007 - Anastasios Melis achieved 15 % energy conversion efficiency by truncation of Chl antenna size.

2008 - Anastasios Melis achieved 25 % efficiency out of a theoretical maximum of 30%.

Short history

SEITE 64

Thanks for your Attention !

Questions ?

Source: http://img.metro.co.uk